Secrecy system of radio broadcast distribution



` E. E. CLEMENTv SECRECY SYSTEM 0F RADIO BROADCAST DISTRIBUTION Dec. ll, 1928.

Filed 0015. 30, 1925 31a/vento@ j EDWARD it".y coLLADAY, 'or Was-Hmefron, nrsrmor onucoLUMB'IAij;

i SECRECYSYSTEM-OF Repro Bnoancas'r nis'rann'ronf Ae'pi'icatip filed october 'i My inventionrelates systems of radio broadcast distributiomand the. present application isa continuation in.,y part of*` myVV 'prior copending' l' application?"` filed October 21, i925, serial` No. 53,977, -patenteduulyl 5,1927, No; 1,635,156.; This inventionhas for its object to provide an organization for the broadcasting of intelligence inqvhich `orderly distribution may vbe secured,'fwith VeryV `briefly' stated, :this -system 'includes subdivision of the. ultimate units or subscribers.; stationsl into local groups in. local areas, each' group related 2toj aj. local I org Vregional dlstributingjstation; the grouping of'these regional*stationsy according to 'district's andrelating veach district group of 1 reginal `stations vto adistrict master station;

the vgrouping of Y,districts into Vdivisions,` Which mayjconveniently coincide with the" geographical standard time divisions of the country; and iinallythe relationof the dis-V trict .masterl stations tolffa central master station.

Y National, district, andl local progra ms `Will subscribers may' select.;- Selection-.is determinedby frequencies, which; by the use; .of

localV exchange, which WillV beV tliefrsame; (for :all -partsf of the country and fOr every Lexchange-down tof the smallest'hamlet, or Vthe` most distant station. In other Words,- every;

subscriber in this system may haveaccess to the entireprogram -availabletoanyother subscriber WithoutregardI to loc' a,tio: n, dis-V alsourceof alternatingcurrentfand comblned tance', time or.circumst ances;

The primary obj ect of my present invention isy secrecy, WithV special' referencefto the .system .of distribution employing double modulation as- .above outlined. Briefly termediate frequency Wave, together with a lated on a short AWave carrier and radiated in the; usual manner.. -The IF vvave"- may also be transmitted over fa jvvire? circuit, -i as EDWARD; n. clamanNT,' oFfWAsi-qrnero1\, Distinct-or coLUMBr,; Assre'noa io authorized personsto "piratetbe `message 180?v toneutraliZeQ the :huin at the subseribeij.s masking Vaudio frequency Wave; for, example fas that due to aO-cyclev 'commercialgenerf Y ator. The-'long orlFwave isthen *modun-V 30, v15525. ,Serial `No., esg'zeoff setforth in my Vapplication above referredi to, andifit will bet understood VinthatcaseV the method of neutralizing the hundv 'vvouldgbe'f' thesame as when thefinessage is transmittey by.-` radiation, l In either` case the receivingf instrument detects; and rectiies. the; carrier f Wave or, Waves, 'and fin kso .doing.gappliesftd .the ,audio kside'of jthe longiwa ve4V Vdetectr alternating .current -of the' samegfrequency as" that., appliedY at f the, transmitter, V in oppo'sit'ephase e., "With aphasef'displacel rment of :1809,Whichjneutralizes the liumj'irrVV thereceiving instrument. mere the1mask;fi ingawavef-is takenfrO-m arfalternating curf rent.fnetv'orlg4 thel neutralizing Waveii's V'p'1ef-:--7 '0 erably taken from the saine netv'vorlnfandf reversed phase. A special gencrater orf.'V f `generators.mayfbegprovided,ghovvever, and- I aln'not to.-be-.lirnitedtoanyfparticular means for producing or .applying the .maske ing'waves; important feature offthe .iii-V ention isthe uselof such 1a masking Wave; on.r a Secondaryor intermediate.'frequencyca rien Wave, in they system enployingfdiiblel modulatio'ny- VThis produces no disturbanceV 80 J V tof-those ,receiving 'otherj modulated aves. .Byemplfiyhe' the' Sameigileiet; fo Slip-l1. plying` :both maskuingfand .neutrallzin S fvva'v'es, changes :in frequency can `.be InadefatYv intervals,sol as to renden it vdifficult '[forfun-l My invention is illustrated'in' the aoco payingdawine in which 'Figure 1V is-adiaf gram showing a transmitting stationfand -receiving:Setonprovided withpn'e format of apparatus and .circuit connections ,for'epr'ac, 1 tising theinventioma dligiQ isfa diagrarn lofla modification therect.''V 'V systemcomprises, 'generallyaanarf f rangement whereby, an audible/ obscuring 95. j 1 Y, il

humis producedbysuitableconnectionwith,,j

With the'audio modulations wtran sinittedso as to rcnderth'e matter so.y transmittedunin-- "..telligible to unauthorized jij listeners,

a v means forsupplyingthe.subscriber?srece1vi ing sets; with alternatinggcurrent from.i ,same/v. source v ,atr a {'phas'e Vljisplacernerlt f of modulations 1 To .:prevent annoying.. non?. p

subscribers who may have ordinaryreceivers V Capablef'ofpickin-stp jor responding.tothe carrier Lvvaves transmitted by the regional'l station, :the obscured signalsaretransrnittedf receiver andv leave '.onlyth'e desired audible fthat previously described soV that the ordinary receiver not equipped 'withfiiieaiisfor double demodulation or detection :vv-illnet respond. VReferring to Figure 1 'in detail,' the reference numeral 400 indicates a pickup microphone supplied with currentfrom va suitable vsource 401 and connected through 403 ofla transformer lator "405, A third winding of a bell ringing transformer 407 whose primary'wiiiding is connected through a connecting plug 108,"suitably shapedV to prevent accidental reversal 'of connections, to a suitablejsource of'alternating current' l'hich. in thepresent instance coiisfistsfof a connection to the mains 109 of 60 cycle alternating current electric power supply 410. Y An audible hum isthus combined with the audio modulations Supplied tothe'imod-V Y fioV At Dji'srfrepresented one offthesevera-l subt f VThe output circuit ulator 405. The audio Ymodulator 405 is connected to the input side of an intermediate frequency oscillator 411 whose modulated outputifs suppliedto an interriiediateV fre-V quency modulator 412-through whichiit is Vmodulated onto,V the waves .generated by. a short wave or radiating oscillator transmitter 413 'connected through coupling 41.4'to thev transmittingmantenna 415.

' The antenna 415V thus transmits Va primary wave'on' which is modulated `a secondary or intermediate frequency superaudio wave on" which inturnv is modulated Qbinationor mixedvwith the audiolwaves'fcr .audible hum producedbythe v@Ofcycle current inthe third Vtran'sforiiier ivinding406.V

scribers stations each of Y which comprises ranrantenna 416 and detector tube 417Z`havingv Y its inputjcircuitI 418.: coupled to the l,antenna y416` and"Y tunedV to `the Y short or :primary Waves transmitted from;f theV antenna v'415. `ofV the detector 417 Vis coupled -to theinput circuit'419 of asecond detector 420 tunedto the-'secondary or intermediate frequency Wave and arrangedto deiftect therefrom the audiomodulations andre- Vproduce the' same iii itsj output circuit- 421 and telephone receiver e A 422 here shownas a pairof head-phones but which of course may be a loud speaker or other audio respon-v sive device.V To neutralize thecycle hum so that'only themodulations produced by the microphone 400 will.' be audible in the receiver 422,the known fact that receiver whose detector filament circuit is supplied with alternating `current produces' a 60 vantage'of by so supplying' the laments fof aiidf'so connecting the the intelligibleV aauiiol waves producedfby the microphone -400, in com-' v Y l 'those receivingstations, cycle hum in its output circuit is` taken ad-v` sired to communicate.V

`na-tingfvarying potentials` tending torprof Ymedulated onto `:thetransmitter at the sendingv station.AV To this endthefilament'circuit 423 is connected' through a transformer 1424` to the. 60Lcyclep'ower supply main 409, Y `the connection with the main 409 being made the primary andv secondary Vwindings 402- v- 404 to an audio moduwinding '406, arranged I in Vthe magnetic circuit. of the traifisformerfr 404 is connected in circuitwith'the primary through aureversing 'or pole changer` switch V425 to enable the ilament current to begrecon'ipletelyV freeofbatteries, the .plate `circuits of the tubes used aresupplied with cur,

Vrent from the main409 through B battery' eliminators 7 any known or othersuitable form 'Except for the substitution ofl power'supply from power mains forthe usual A1 and B bat# teries, theV receivingcircuitfjustb described y y is-the sameas the receiver for` double modu- -latioir shown in the Vpublication entitled cPrinciples of VRadio,Communication by J.- H. MorecroftypageSS; Where-amplifi'` cation of the intermediate frequency `wave is desired; suitable amplifying meansfmay be inserted between the two detector tubes417 420 intlie spacebetween the dotted lines.;j

VReferringyto Fig. 2,/ the [vacuum Atube detectors yare show nnprovided withftheqrdinary A andB batterieslwhile thefs'econdf ary circuit ef the bell ringingltransformei' 40( is connectedthroughla coupler'407?V with the plate circuit ofthe second detector 420.

To make the Y receiving station Y This' obviates anyl liability to la harmonic" or other distorted generation in the detector circuitY due 'to theuse: ofW` altern ating current on the filament?V It should'be noted in'addition;V that suitable VVrregulating devices are contemplated whereverfneeded in the system, 'as well vas phase adjusting devices 'and vsuch Yother'expedients known in the arts as Vmay' be? necessary te VVpractice the invention successfully.

Iclaim: g 'i ,1.1 The 'method of secretisignaling comprises controlling Vthe f action] of `signal transmitting apparatus soas Vto produce a signal modulated wave carrying also asa masking modulation oneV Vof two complementary components which when added together will produce 1 a 4zerol Vor silent, wave, broadcasting Vthe `sigiial""modulated wave "with its said masking ,modulatioiig and separately supplying the other or complementary component'by point topQint transmission to 1 in thejfield-of said broadcast component, with vv vhic'li it is "de- 2. Afs'ecre'cy system: of broadcast distri- Vbution comprising a transmitting apparatus izo r quency current, meansf for radiating' Said' of said loW frequency currentto` those'fretriloutionV 'comprising radio 'transmitting' WaveWitha signal, and alsoWith-one phase or complementary component Aof a lc'nvj`:ti`"ey compound or masked signal Wave,` means for receiving said Wave, andfmeans to supply by point lto point transmission the; second phase' or complementary component ceiving, stations only, inthe field ofHV said broadcast componen@ sired to cornnnmicate.'` v e 3. Asecrecyvsystem'of radio broadcast' dis` means arrangedto radiate Waves .carrying desired audio modulations l andl alsol rcarryingv 'masking audio modulationgmeans for point to point transmission4 in the field of said radiation of Waves complementary to, said masking Wavesu'orjmodulations, and means for receivii'ig'said-V radiated Wavesand for'combiningl therewith i' the... field fof Yradiation mimicationfis v desired ij 1 A'current loutv of oppovsitezfphasegto' themaskeg; f ingy component #of :the f modulations 'receiizeil vith'Wiiieiiiit iside; f

4in current for?` masking f impulses L is taken T Y h V u network and* the complementary lcurrelt'for -re'ceiVing-stations isftaken,iomlotlierfpai'ts .of tlievelectfric` lightnetwork anywherev :Waves/,fat those `stations *l kwith Whiclcom.-

4. Asecrecy system Y*as claimed inc1ai1n"3,i 'in whichl the masking impulses are@periodicVV er N audio frequency-modulationsand the receiviQ-`VV ingmeans atv desired stations in-V the iield'of l l A- .y radiation i'syrsup'plied VWitliithesaine periodic'k 301 by' radiation. Y

V5." A secrecyfsystenifas claim-ed Vclaim `rom onefportion'zof `an electric `liglit cancellingfout said maskingimpulsesat theV in theffieldfofradiation. y 'l' a A In .testimony whereof l hereuntor ai'Xfmy, Y

*Y l Y i' a /V 5;] EDWARD iE. CLEMEN 

